We have discussed the hip implant, THA and its related vibration assessing technique. So, now, what about the knee joint? Is it different from the hip? What is the difference? And what are the similarities that we can take advantage of in surgery of bad knee joints?
Principally, TKA, a surgical procedure to replace the weight-bearing surfaces of the knee joint with a prosthesis, is more or less the same as THA. Old people who suffer from diseases such as osteoarthritis or rheumatoid arthritis will come across the problem of pain in their knee joint, as well as a reduction of range of motion. In the USA, more than 230,000 TKA’s are performed every year. Of all these surgeries, approximately 5 to 10% of the prostheses need to be replaced within 10 to 15 years due to the worn-out connections between implant and bone. Either loosening or infection can cause bad connections.
Two photos are displayed to give a first impression of the hip implant and knee implant.
There are several methods currently used in detect the worn-out of medical implants, including physical examination, radiography(most widely used), laboratory tests, and vibration techniques (latest). Physical examination is a relative subjective and inconclusive assessing method, and laboratory tests mainly focus on the diagnosis of infection in the bone.
Radiography is the most classic way of loosening diagnosis. It is used to evaluate prosthesis alignment, fixation,gross polyethylene wear and quality of periprosthetic bone. But it is subjective, inconclusive and less sensitive( e.g., a sensitivity of 83% has been reported for the tibial component and a specificity of 72%).
Vibration analysis has been used to determine bone mechanical properties, to monitor fracture healing, and to assess the stability of dental implants. It is also used to assess the initial stability of the femoral THA component, intra-operatively. Two differences exist between a TKA and a THA. Firstly, knee joint is not accessible, so a small incision should be cut to use vibration test post-operatively. Secondly, in THA, vibration technique is used to as a comparison between two succeeding insertion stages during surgery as a comparative method, while in TKA it is used in an absolute way.
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Marx A, Saxler G, Landgraeber S, . Comparison of subtraction arthrography, radionuclide arthrography and conventional plain radiography to assess loosening of total knee arthroplasty. Biomedizinische Technik, Vol 50, No 5, p 143-147, 2005.
Pastrav L, Monitoring of the fixation of orthopaedic implants by vibration analysis, promoters G. Van der Perre, R. Van Audekercke, 28 October 2010.
Pastrav L, Jaecques S, Mulier M, Van der Perre G. Detection of the insertion end point of cementless hip prostheses using the comparison between successive frequency response functions. J Applied Biomat & Biomech, Vol 6, No 1, p 23-29, 2008.